PARIS, July 11 (Reuters) - French utility EDF said on Thursday that the extension of outages at its Flamanville 2 and Paluel 4 nuclear reactors was due to a series of technical issues.

Both reactors are undergoing their third 10-year upgrade, and have been offline since early January.

They were due to resume production on Aug. 16 for Flamanville 2 and July 31 at Paluel 4 but the outages have since been extended for an additional period of time.

A notice from French electricity grid operator RTE said on Thursday that the reactors are now due to resume production on September 9 at the 1,300 megawatt (MW) Paluel 4, and on October 15 at the similar capacity Flamanville 2.

A spokesman for EDF said a succession of unforeseen technical issues forced the company to delay the planned restart of the reactors.

There were no serious issues at Flamanville, he said. Paluel 4, however, faced a critical electro-mechanical issue with a diesel generator that would require some time for repairs, he said.

EDF is carrying out a 10-year overhaul at seven of its 58 nuclear reactors in France this year, slightly higher than the average five it does every year, the spokesman said, denying reports suggesting it was short of critical skills.

He added that the company had reduced the number of days reactors are delayed before resuming production to 14 days on average last year from around 20 days in 2017, and was able to bring back its Cattenom and St Alban reactors on time.

The spokesman said the prolonged delays at Paluel and Flamanville would allow the utility enough time to sort out any other issues that cropped up.

Alongside Paluel 4 and Flamanville 2, EDF started the fourth 10-year upgrade at its 900 MW Tricastin 1 reactor on June 1, to ready it for approval to operate beyond its 40-year lifespan.

Upgrade works are also being carried out at the 1,500 MW Chooz 2, the 1,300 MW Nogent 1, the 1,300 MW Belleville 2 and the 900 MW Chinon 3 reactors. (Reporting by Bate Felix, editing by Deepa Babington)